The designers of electronic devices, in particular mobile electronic devices, strive to create a rich, convenient, fast, and intuitive user interface. Providing feedback to a user who is interacting with a tool or device by the use of one or more fingers in the form of haptic feedback is useful towards these goals.
One form of haptic feedback is a mechanical click, motion, detent, or mechanical click. Most full-size and traditional keyboards provide a nonlinear keystroke excursion that gives this form of feedback. Another form of haptic feedback is a rhythmic shaking or vibration, sensed by a finger, hand, or other part of the body. For example, a fingertip may be used on a touch screen for data-input or feedback. Flight controls include a stick shaker.
One traditional method of generating haptic feedback comprises spinning an out-of-balance weight. Another traditional method comprises an electromagnetic coil, or solenoid, to move an object that the user feels. The movement may be a single movement or it may be a repetitive movement which may be detected by the user as a vibration.
One form of prior art uses a small motor that includes an armature, copper wire winding(s), a rotating shaft, an elliptical or non-symmetric weight, and a power and control source. When the motor turns, the non-symmetric weight is spun or oscillated, which produces a vibration that either directly or indirectly is applied to a portion of the equipment or host device. The user then feels the oscillation or vibration. A disadvantage of this design is startup delay. Another disadvantage with this design is that the range of haptic feedback is limited to a single or small number of fixed frequencies. A third disadvantage is its relatively large size. A fourth disadvantage is relatively high cost that prevents practical applications that involve a large number of haptic devices within one piece of equipment. A fifth disadvantage is poor reliability. A sixth disadvantage is that only regular vibration may be produced.
In one embodiment of the current invention a working fluid inside a sealed vessel is vaporized to create a pressure increase with phase change. The pressure change causes mechanical motion. The working fluid may be vaporized in this way repeatedly, condensing in the intervening time intervals, causing a controlled haptic motion or vibration. There are some similarities of this approach with the method of creating ink droplets in ink jet print heads in which droplets are piezoelectrically vaporized to jump off of the print head or electroresistively heated to vaporize off the head.
In the current invention, in one embodiment, the working fluid is vaporized and condensed repeatedly to create a pressure/volume change with excursion and frequency that may be interpreted by touch or motion sensors in the skin or secondary muscle sensors in the body. This cycle also occurs in heat pipes, for a different inventive advantage.
In portable or mobile electronics, cost, space, reliability and power become major design issues. Advantages of this invention include lower cost, smaller size, more reliable operation, and less power consumption than traditional methods of generating haptic feedback.